Regarding a liquid chromatograph (LC) in which a multichannel-type detector such as a photo diode array (PDA) detector is used as a detector, an injection time of a sample to a mobile phase is provided as a starting point, and an absorbance spectrum is repeatedly obtained with respect to an eluate from a column, thereby acquiring three-dimensional chromatogram data having three dimensions of time, wavelength, and absorbance. FIGS. 15A and 15B represent the schematic views of the aforementioned three-dimensional chromatogram data. Data on a specific wavelength is extracted from the three-dimensional chromatogram data, thereby generating a wavelength chromatogram indicating a relation of time and absorbance in terms of the specific wavelength. Also, data at a specific time is extracted from the aforementioned three-dimensional chromatogram data, thereby generating an absorbance spectrum indicating a relation of wavelength and absorbance at the specific time.
It is noted that when quantitative analysis of a sole component included in a sample is performed, a flow injection analysis (FIA), in which a column is not used (that is, component separation is not performed), may be used. The FIA method is a method in which a predetermined amount of a sample is injected into a mobile phase being supplied at a constant flow rate by use of an injector for liquid chromatograph, and the sample is introduced to a detector along with the flow of the mobile phase. As is the same with column eluate in a case where the column is used, the concentration of a target component changes in an approximately inverted V-shape with a lapse of time. Data obtained in the case where the sample introduced by the aforementioned FIA method is detected by the multichannel-type detector is also three-dimensional data having three dimensions of time, wavelength, and absorbance, and practically the same with data collected by the liquid chromatograph described above. Accordingly, “three-dimensional chromatogram data” in the present specification includes the three-dimensional data collected by the FIA method.
Regarding the aforementioned liquid chromatograph, when the quantitative analysis on a known target component is performed, generally, a wavelength chromatogram at an absorption wavelength in accordance with the target component is obtained, and a quantitative value is calculated by collating a calibration curve with an area (or height) of a peak originating from the target component that is emerged on the chromatogram.
When the target component is quantitated, there is no problem when the peak emerged on the wavelength chromatogram originates from only the target component. However, a peak is not always based on a sole component (target component), but in some cases, unexpected impurities are included. Accordingly, peak purity determination processing, in which it is examined whether the peak emerged on the chromatogram originates from only the target component or includes impurities, has been performed.
For example, Patent Literature 1 discloses a peak purity determination processing technique for chromatograms obtained by the liquid chromatograph for which the multichannel-type detector is used. In this technique, an absorbance spectrum at a time T0 in accordance with the peak apex of a target peak on the wavelength chromatogram is represented as S0 (λ), and an absorbance spectrum at an arbitrary time T prior to or subsequent to the time T0 is represented as S (λ), and a coincidence degree P between S0 (λ) and S (λ) is calculated by the following formula (1):
                    P        =                              ∑                                                            S                  0                                ⁡                                  (                  λ                  )                                            ·                              S                ⁡                                  (                  λ                  )                                                                                        ∑                                                                    S                    0                    2                                    ⁡                                      (                    λ                    )                                                  ·                                  ∑                                                            S                      2                                        ⁡                                          (                      λ                      )                                                                                                                              (        1        )            
Then, as is illustrated in FIGS. 16A and 16B, the target peak is displayed in such a manner as to be divided along the temporal axis by color in accordance with the coincidence degree P with respect to the peak apex (expressed by shading in the diagram), e.g., in green when the coincidence degree P is from 1.0 to 0.8, or in yellow when the coincidence degree P is from 0.8 to 0.6, or in orange when the coincidence degree P is equal to or less than 0.6.
When the target peak originates from only the target component, as illustrated in FIG. 16A, the coincidence degree P increases in the vicinity of the peak apex and decreases as it moves away from the peak apex, and its shape is approximately symmetrical with respect to the central axis of the peak. In contrast, when another peak exists prior to or subsequent to the peak apex of the target peak (that is, when the target peak includes impurities), the coincidence degree P decreases prior to or subsequent to the peak apex of the target peak. In the example illustrated in FIG. 16B, for example, the coincidence degree P on the right side (on the delayed side in the temporal order) interposing the peak apex is low, compared with the coincidence degree P on the left side. Accordingly, it can be determined that there is a high possibility that impurities are included in the vicinity of the temporal range.
However, regarding the aforementioned conventional peak purity determination method, when the peak of impurities exists in close proximity to the peak apex of the target peak, the coincidence degree P hardly decreases in the proximity of the peak apex, so that there has been a case where the existence of the impurities cannot properly be detected.
Also, regarding the aforementioned peak purity determination method, as disclosed in Non-Patent Literature 1, it is necessary to set a noise vector, for example, whose components are magnitude of noise at each wavelength, as a parameter, in obtaining the threshold of the coincidence degree P for determining whether an impurity peak is included. The problem here is that, in order to obtain the noise vector, the magnitude of noise in a predetermined wavelength area detected by the multichannel-type detector should be successively monitored, and complicated computations of standard deviation in temporal change of the noise in the predetermined wavelength area is required.